1. Field of the Invention
The present invention relates to a system, method, and computer program product for instructing allocation of a plurality of exposure units, and particularly, to the use of a mix-and-match technique for properly allocating exposure units according to exposure processes.
2. Description of Related Art
Manufacturing processes to produce electronic devices such as semiconductor devices and liquid crystal devices usually include photolithography processes. Photolithography processes include a thin-film process to form a photo resist film from photosensitive resin, an exposure process to expose the photo resist film, and a development process to develop the exposed photo resist film. The exposure process precisely transfers mask patterns at a given resolution onto a photo resist film formed on a substrate.
For the purpose of obtaining high productivity and efficiency, an electronic-devices manufacturing factory simultaneously runs many exposure units so as to process a large number of substrates in parallel. In such a case, the same substrate may be repeatedly processed by different exposure units in different exposure processes to form various exposure patterns thereon. The exposure units have individual stage and lens characteristics, and therefore, it is difficult to precisely overlay exposure patterns one upon another at a given resolution on the same substrate. To solve this problem, a related art selectively uses exposure units for different exposure processes depending on the stage and lens characteristics of the exposure units. This technique is called a “mix-and-match” technique. The mix-and-match technique computes an overlay correction value applied to a first exposure unit to be used in a first exposure process according to a second exposure unit used in a second exposure process. The overlay correction value is applied to the first exposure unit, to cancel differences in stage and lens characteristics between the first and second exposure units.
According to the related art, the second exposure process is a past process already completed, and the first exposure process is a current or future process not yet begun. Namely, the related art achieves the mix-and-match technique based on an exposure unit used in a completed past process, in order to select an exposure unit for a current or future process. If the second exposure process is not a past process, i.e., has not yet been carried out, there will be no way for the related art to compute an overlay correction value for the first exposure unit.